Objectives: 1. To develop and validate new methods for studying the enterohepatic circulation of bile acids in man in health and disease. 2. To characterize bile acid metabolism in health and selected diseases. 3. To develop new diagnostic tests for altered bile acid metabolism. 4. To explore poorly understood areas of the enterohepatic circulation. Goals for the current year (1973): 1. Methods for studying the EHC of BA in man. a. Bile acid kinetics; 1) To develop a mathematical description of the enterohepatic circulation. 2) To develop a non-invasive procedure for the determination of bile acid kinetics. 3) To validate 2,3, H3-labeled bile acids for measurement of bile acid kinetics. b. Measurement of bile acid mass; 2. Characterization of bile acid metabolism in health and disease. a. To define metabolism of steroid and amino acid moiety of taurine conjugated bile acids. b. To define metabolism of steroid moiety of appropriate primary and secondary bile acids in selected diseases. 1) In patients with cholelithiasis before and after feeding chenodeoxycholic acid. 2) In cholecystectomized subjects. c. To measure secretion of biliary lipids; 1) In age and sex matched healthy controls receiving no medication. 2) In patients with cholesterol cholelithiasis. 3. In patients with cholelithiasis receivng chenodeoxycholic acid. 3. Exploration of poorly understood areas of the enterohepatic circulation. a. To gain insight into the mechanism of bile formation. 1) Development of an ex vivo perfused canine liver preparation. 2) Comparison of the effect of cholyltaurine with that of chenodeoxycholyltaurine on biliary lipid secretion by the ex vivo perfused canine liver. 3) Search for a humoral regulation of bile acid synthesis.